6- Noise and Interference

Question 1

Site the 4 sources and causes of artefacts

Answer 1

Movement, electrical stimulation (stimulation artifact), other electrical devices or interferences(=Signals due to non ideal properties of components and devices).

Question 2

Which factor can determine signal to noise ratio ?

Answer 2

The amount of muscle/nerve or fatty tissue. Fat alter the impedance.

Question 3

Site interferences classification

Answer 3

Origin (in the recording sys or external interference sources)
electrode noise
amplifier noise
malfunctioning devices
mvt artefacts
eletrostatic and electromagnetic interf
HF (radio) interf

Question 4

Site the three main external interferences

Answer 4

Low F interf (electric and magnetic field are not copled, near field, various mechanisms)
High F interf
-Interf caused by other biological signals)

Question 5

For which type of Fs Maxwell equations have to be taken into account ,?

Answer 5

for high F interf because electric and magnetic field are coupled

Question 6

Site the 4 types of interference due to tools .

Answer 6

Galvanic, Capacitively, inductively and line waves.

Question 7

Site the object, the interfering quantity and by what is coupled by “galvanic interf”.

Answer 7

reference conductor - i or di/dt - Z

Question 8

Site the object, the interfering quantity and by what is coupled by “capacitive interf”.

Answer 8

Signal conductor - du/dt - C

Question 9

Site the object, the interfering quantity and by what is coupled by “inductive interf”.

Answer 9

Signal conductor - di/dt - M (magnetic field)

Question 10

Site the common coupling impedances for different galvanic interferences (low F, High F, rising F)

Answer 10

Low : R and C dominates
High F, L dominates (and r)
Rising F : L outweighs R and C.

it means if we want low F and have galvanic inter we can get rid of R and/or Cs (cut them out of the circuit)

Question 11

Site the solution to reduce galvanic interferences

Answer 11

Separate common conducting paths

decoupling (optocoupler or transformer)

Question 12

what can we modify on capacitors to decrease capacitive interferences.

Answer 12

increase the distance or redcethe size to minimize the capacitor (= reduced coupling capacity with small ssurfaces, larger distances or oncentrated design of the recording sys)

Question 13

Site ways to reduce capacitive interferences.

Answer 13

Amplitude reduction of the interfering qtt
low resistance design of the recording sys (Une low)
Reduced coupling capacity
Symmetric coupling capacities
bootstaping
shielding

Question 14

what can we shield to reduce capacitive coupling ?

Answer 14

Interference source/recording sys or recording setup.

Question 15

describe by 3 steps the principle of the driven right leg

Answer 15

common mode voltage reudction, summation and coupling of current, disturbance current Idk gets compensated.

Question 16

Site ways to get rid of inductive disturbance.

Answer 16

1-reducing the sources of inductive disturbances
-low signal intensity and slope, low signal setup, concentrated setup with space separation to the recording sys.
2-reducing the inductive coupling
concentrated sys, large distance to the disturbing sys, symmetric setup and avoid parallel tracks,, field dcoupling by small track areas,
damping the magnetic field with shielding.

Question 17

site example to get rid of inductive disturbance

Answer 17

twisting cables, symmety, shielding with specific materials, measuring with a dipole antenna .